Stripe Rust Forecast for the
Pacific Northwest
Xianming Chen, 3/12/06
As
the spring is around corner, many of you may be wondering if we will have
stripe rust problem this year.
We
have conducted stripe rust forecast using predication models based on the
winter temperatures. I have presented
the forecast results in the Wheat Research Progress Report meeting and seminars
for growers. The results were also presented by Scott Yates in his article
"Rust Expected to Hit Later This Year" on Capital Press (February 24,
2006)
The
forecast results, shown in the following figure indicate that stripe rust will
be likely developed to the highest level (100% severities) on susceptible
varieties by the milk stage, as severe as last year.
Although
the forecast model indicates as equally severe stripe rust for 2006 as it was
in 2005, the disease will started later (at lease 2-3 weeks) in 2006. This is because of the following two factors. First, because of the lack of the moisture in
last fall during the planting time, most of winter wheat fields in the Horse
Heaven Hills and the Connell area were planted later (in October). These areas are the hot spots to catch stripe
rust infection before winter. The late planting should have reduced stripe rust
infection before the winter. Secondly,
the cold weather in last December prevented further development of stripe rust
during the winter. As I checked these
areas in February, the plants were generally small and stripe rust was not
found. This is different from the
2004-2005 winter, during which rust was continuing developing in the area of
Horse Heaven Hills. The cold period in
mid February has slowed winter wheat growth and also should have slowed rust
development infected plant tissue. Therefore, based on the forecast model and
these considerations, we will likely have another severe stripe rust year in
the PNW, but the disease will certainly start later than last year and the
damage should not be as great as last year because the initial rust pressure
will not be as high as last year and the growth period for stripe rust
development will be shorter in 2006.
However, stripe rust is capable of quickly developing and spreading if
temperatures and moistures are favorable for the rust. A great concern is that some
new races of the fungus detected last year are more virulent. The appearance of the new races and increase
of some races detected in 2003 and 2004 has rendered several spring wheat
cultivars, including WPB 926, IDO377s, Hank, and Tara susceptible, and this
group of cultivars will be more vulnerable to stripe rust in 2006. Please refer the updated Seed Buyer's Guide
for choosing resistant and moderately resistant spring varieties to grow.
If
you grow susceptible winter and spring wheat varieties, you definitely need to
check your fields in late spring and get prepared for use of fungicides. We expected to see stripe rust in most part
of the eastern PNW in May.
Wheat
stripe rust has been reported in
Louisiana
,
Texas
, and
Arkansas
,
even through not as severe as this time of the last year. Leaf rust is widespread in the Great Plains,
from
Texas
to
Nebraska
.
Fig.
1. Stripe rust forecast for 2006 based
on temperatures in December, 2005 and January 2006 and comparison with
temperatures and stripe rust levels of 2000-2005 and the "normal year of
temperature". The "normal temperatures"
are those from 1949 to 2005. A: Average
monthly temperatures for December and January.
B: Disease levels. The bars indicate predicated disease levels based on
winter temperatures and the values (in blue) show the actual stripe rust level
occurred on susceptible varieties in our experimental fields. Even through the temperatures and disease
levels are those of Pullman,
WA. The predication is generally applicable to
the eastern PNW.
